Fluorescent lamp is a very popular way of lighting. It has the advantages of high efficacy, long service life and does not emit much heat through radiation. The lamp, however, has to be started by introducing a high ignition voltage across it. There are many starting scheme for fluorescent lamps by using an electronic ballast. One popular type of electronic ballast is the instant-start ballasts.
The instant-start type ballast features almost immediate start of the lamps when the AC power is applied to the ballast. It does not require a starter device or circuit. It consumes less energy during operation and thus it is more efficient. However, as the lamp is started with a brute force by building a very high ignition voltage to the lamp, frequent on-and-off switching of the lamp will decrease the useful service life.
Therefore instant-start type ballasts are the most useful in applications where very long time of continuous lighting is anticipated. With many other advantages such as simple installation and the capability of independent lamp operation, i.e., when one of the lamps is worn out or removed, the remaining lamps can still operate normally, the instant-start type ballast enhances safety and the ease of maintenance.
For an instant-start type ballast, it is not uncommon to see an ignition voltage going as high as 600V-1000V peak and more. In cases such as individual lamp removal during maintenance while the AC power is still applied to the ballast, or the lampholder being aged, sporadic open circuit in the lampholder may occur. As a result, a high voltage will be induced and cause arcing. Arcing is a very high energy path of plasma discharge when electrical breakdown of air occurs under a very high potential difference. Arcing inside the lampholders is not favorable, as the resultant high temperature can melt the plastic housing and cause the exposure of metallic contacts and even cause a fire. Moreover it will degrade the contacts and over-stress the components inside the ballasts.
Therefore, recently global product safety certification agencies such as the Underwriters Laboratories (UL) have introduced a class of “Type CC” (short for Commercial Cabinets) ballasts that are designed to minimize arcing within the lampholder. Since then many lighting ballast manufacturers start to design “Type CC” ballasts with anti-arcing protection, or non-arcing fluorescent lamp holders. The usual approach is to sense abnormal voltage and/or current inside the ballast circuit to detect the occurrence of arcing, and cease the ballast operation once the condition is confirmed. They usually involve active devices and even micro-controllers. Thus, a more cost-effective and miniature solution is needed so that the additional components can fit into the existing casings.